Turbomachines are machines that transfer energy between a rotor and a fluid. For example, a turbomachine may transfer energy from a fluid to a rotor or may transfer energy from a rotor to a fluid. Two examples of turbomachines are a power turbine, which uses the rotational energy of the rotor to do useful work, for example, generating electrical power; and a turbocharger, which uses the rotational energy of the rotor to compress a fluid.
Turbochargers are well known devices for supplying air to an inlet of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing connected downstream of an engine outlet manifold. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to an engine inlet manifold. The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housings.
The turbine of a conventional turbocharger comprises: a turbine chamber within which the turbine wheel is mounted; an annular inlet defined between facing radial walls arranged around the turbine chamber; an inlet volute arranged around the annular inlet; and an outlet passageway extending from the turbine chamber. The passageways and chamber communicate such that pressurized exhaust gas admitted to the inlet volute flows through the inlet to the outlet passageway via the turbine and rotates the turbine wheel. It is also known to improve turbine performance by providing vanes, referred to as nozzle vanes, in the inlet so as to deflect gas flowing through the inlet. That is, gas flowing through the annular inlet flows through inlet passages (defined between adjacent vanes) which induce swirl in the gas flow, turning the flow direction towards the direction of rotation of the turbine wheel.
Turbines may be of a fixed or variable geometry type. Variable geometry turbines differ from fixed geometry turbines in that characteristics of the inlet (such as the inlet's size) can be varied to optimize gas flow velocities over a range of mass flow rates so that the power output of the turbine can be varied to suit varying engine demands. For instance, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel is maintained at a level which ensures efficient turbine operation by reducing the size of the inlet using a variable geometry mechanism. Turbochargers provided with a variable geometry turbine are referred to as variable geometry turbochargers.
Nozzle vane arrangements in variable geometry turbochargers can take different forms. Two known types of variable geometry turbochargers are swing vane turbochargers and sliding nozzle turbochargers.
Generally, in swing vane turbochargers the inlet size (or flow size) of a turbocharger turbine is controlled by an array of movable vanes in the turbine inlet. Each vane can pivot about an axis extending across the inlet parallel to the turbocharger shaft and aligned with a point approximately half way along the vane length. A vane actuating mechanism is provided which is linked to each of the vanes and is displaceable in a manner which causes each of the vanes to move in unison, such a movement enabling the cross sectional area available for the incoming gas and the angle of approach of the gas to the turbine wheel to be controlled.
Generally, in sliding nozzle turbochargers the vanes are fixed to an axially movable wall that slides across the inlet. The axially movable wall moves towards a facing shroud plate in order to close down the inlet and in so doing the vanes pass through apertures in the shroud plate. Alternatively, the nozzle ring is fixed to a wall of the turbine and a shroud plate is moved over the vanes to vary the size of the inlet.
The compressor of a conventional turbocharger comprises a compressor housing defining a compressor chamber within which the compressor wheel is mounted such that it may rotate about an axis. The compressor also has a substantially axial inlet passageway defined by the compressor housing and a substantially annular outlet passageway defined by the compressor housing between facing radially extending walls arranged around the compressor chamber. A volute is arranged around the outlet passageway and an outlet is in flow communication with the volute. The passageways and compressor chamber communicate such that gas (for example, air) at a relatively low pressure is admitted to the inlet and is pumped, via the compressor chamber, outlet passageway and volute, to the outlet by rotation of the compressor wheel. The gas at the outlet is generally at a greater pressure (also referred to as boost pressure) than the relatively low pressure of the gas which is admitted to the inlet. The gas at the outlet may then be pumped downstream of the compressor outlet by the action of the compressor wheel.
It is known to provide a turbocharger turbine with a valve controlled bypass port referred to as a wastegate, to enable control of the turbocharger boost pressure and/or shaft speed. A wastegate valve (typically a poppet type valve) is controlled to open the wastegate port (bypass port) when the boost pressure of the fluid in the compressor outlet increases towards a pre-determined level, thus allowing at least some of the exhaust gas to bypass the turbine wheel. Typically the wastegate port opens into a wastegate passage which diverts the bypass gas flow to the turbine outlet or vents it to atmosphere.
The wastegate valve may be actuated by a variety of means, including electric actuators, but is more typically actuated by a pneumatic actuator operated by boost pressure delivered by the compressor wheel. The wastegate valve actuator is typically connected to the wastegate valve by a linkage, part of which passes through an actuation conduit in the turbine housing. Where the linkage passes through the actuation conduit it is possible that fluid from the turbine outlet may leak into the actuation conduit and then to atmosphere. Leakage of fluid from the turbine outlet to atmosphere may have an adverse effect on the performance of the turbine and hence turbocharger.
According to a first aspect of the present disclosure there is provided a turbine comprising a turbine housing defining a turbine inlet upstream of a turbine wheel and a turbine outlet downstream of the turbine wheel; a wastegate passage connecting the turbine inlet and the turbine outlet; a wastegate valve comprising a movable valve member; the wastegate valve having an open state in which gas may pass between the turbine inlet and turbine outlet via the wastegate passage and a closed state in which the valve member substantially prevents gas from passing between the turbine inlet and the turbine outlet via the wastegate passage; and wherein the valve member is mounted to an actuation member, the actuation member passing through an actuator conduit of the turbine housing, and being movable so as to move the wastegate valve between the open and closed states; the turbine further comprising a sealing arrangement configured to provide a seal arranged to substantially prevent gas from passing from the turbine outlet into the actuator conduit; wherein the sealing arrangement is configured such that when the valve member of the wastegate valve is urged into the closed state by the actuator member the sealing effectiveness of the sealing arrangement is increased.
The wastegate valve may further comprise a valve seat, the valve member contacting the valve seat when the wastegate valve is in the closed state; wherein the actuation member has a longitudinal axis; and wherein the valve seat is angled relative to the longitudinal axis and is configured such that when the actuation member urges the valve member of the wastegate valve into the closed state, the valve seat imparts a force on the valve member which urges the valve member in a first substantially axial direction, and wherein the sealing arrangement is configured such that the urging of the valve member in the first substantially axial direction increases the sealing effectiveness of the sealing arrangement.
The valve member may comprise a surface configured such that, in use, when the wastegate valve is in said open state, gas which passes through the wastegate passage is incident on said surface of the valve member, and wherein the sealing arrangement and valve member are configured such that gas incident on said surface applies a force to the valve member which increases the sealing effectiveness of the sealing arrangement.
The actuation member may have a longitudinal axis and wherein a normal to said surface is non-perpendicular to the longitudinal axis of the actuation member; and the valve member further being configured such that, in use, when the wastegate valve is in said open state, gas which passes through the wastegate passage is incident on said surface of the valve member, the gas incident on said surface applying a force to the valve member which urges the valve member in a first substantially axial direction which increases the sealing effectiveness of the sealing arrangement.
The actuation member may rotate in order to move the wastegate valve between the open and closed states.
The actuator may rotate about its longitudinal axis in order to move the wastegate valve between the open and closed states.
The valve member may be mounted to the actuation member such that the valve member is located on a first side of the actuator conduit, and a portion of the actuation member is mechanically linked to an actuator or linkage configured to be linked to an actuator, wherein the portion of the actuation member which is mechanically linked to the actuator or linkage configured to be linked to the actuator is located on a second side of the actuator conduit.
The sealing arrangement may comprise a seal member.
The sealing arrangement may be configured such that the urging of the actuation member in the first substantially axial direction compresses the seal member.
The seal member may be disposed upon the actuation member.
The seal member may be sandwiched between the valve member and the turbine housing.
The turbine may further comprise a bush, the bush being received by the actuator conduit and the actuation member passing through the bush, and wherein the seal member is sandwiched between the valve member and the bush.
According to a second aspect of the present invention there is provided a turbocharger or power turbine including a turbine according to the first aspect of the present invention.